Bio::DB::GFF::Aggregator::so_transcript is identical to the processed_transcript aggregator, which was designed to be compatible with the Sequence Ontology canonical gene. It aggregates raw "exon," "CDS", "five_prime_UTR", "three_prime_UTR", "transcription_start_site" and "polyA_site" features into "mRNA" features. The UTRs may also be named "untranslated_region," "five_prime_untranslated_region," "three_prime_untranslated_region,", "5'-UTR," and other synonyms.

The processed_transcript aggregator is loaded by default, so this is only needed for backward compatibility.